Heat pump and cascaded caloric regenerator assembly

ABSTRACT

A heat pump, as provided herein, may include a hot side heat exchanger, a cold side heat exchanger, a pump, and a caloric heat pump. The caloric heat pump may include a regenerator housing, a plurality of stages, and a field generator. The regenerator housing may extend along an axial direction between a first end portion of the regenerator housing and a second end portion of the regenerator housing. The plurality of stages may be arranged sequentially along the axial direction from the first end portion to the second end portion. The plurality of stages may be arranged so that caloric temperature peaks of the plurality of stages increase along the axial direction according to a predetermined, non-linear curve. The field generator may be positioned adjacent to the plurality of stages to subject the plurality of stages to a variable field generated by the field generator.

FIELD OF THE INVENTION

The present subject matter relates generally to heat pumps, such asmagneto-caloric heat pumps, for appliances.

BACKGROUND OF THE INVENTION

Conventional refrigeration technology typically utilizes a heat pumpthat relies on compression and expansion of a fluid refrigerant toreceive and reject heat in a cyclic manner so as to effect a desiredtemperature change or transfer heat energy from one location to another.This cycle can be used to receive heat from a refrigeration compartmentand reject such heat to the environment or a location that is externalto the compartment. Other applications include air conditioning ofresidential or commercial structures. A variety of different fluidrefrigerants have been developed that can be used with the heat pump insuch systems.

While improvements have been made to such heat pump systems that rely onthe compression of fluid refrigerant, at best such can still onlyoperate at about forty-five percent or less of the maximum theoreticalCarnot cycle efficiency. Also, some fluid refrigerants have beendiscontinued due to environmental concerns. The range of ambienttemperatures over which certain refrigerant-based systems can operatemay be impractical for certain locations. Other challenges with heatpumps that use a fluid refrigerant exist as well.

Magneto-caloric materials (MCMs) (i.e., materials that exhibit themagneto-caloric effect) provide a potential alternative to fluidrefrigerants for heat pump applications. In general, the magneticmoments of MCMs become more ordered under an increasing, externallyapplied magnetic field and cause the MCMs to generate heat. Conversely,decreasing the externally applied magnetic field allows the magneticmoments of the MCMs to become more disordered and allow the MCMs toabsorb heat. Some MCMs exhibit the opposite behavior (i.e., generatingheat when the magnetic field is removed)—such MCMs are sometimesreferred to as para-magneto-caloric material, but both types arereferred to collectively herein as magneto-caloric material or MCM. Thetheoretical Carnot cycle efficiency of a refrigeration cycle based on anMCMs can be significantly higher than for a comparable refrigerationcycle based on a fluid refrigerant. As such, a heat pump system that caneffectively use an MCM would be useful.

Challenges exist to the practical and cost competitive use of an MCM,however. In addition to the development of suitable MCMs, equipment thatcan attractively utilize an MCM is still needed. Currently-proposedequipment may require relatively large and expensive magnets, may beimpractical (e.g., for use in appliance refrigeration), and may nototherwise operate with enough efficiency to justify capital cost.

Accordingly, a heat pump system that can address certain challenges,such as those identified above, would be useful. Such a heat pump systemthat can also be used in a refrigerator appliance would also be useful.

BRIEF DESCRIPTION OF THE INVENTION

Aspects and advantages of the invention will be set forth in part in thefollowing description, or may be obvious from the description, or may belearned through practice of the invention.

In one exemplary aspect of the present disclosure, a heat pump isprovided. The heat pump may include a hot side heat exchanger, a coldside heat exchanger, a pump, and a caloric heat pump. The pump may beoperable to flow a working fluid between the hot and cold side heatexchangers. The caloric heat pump may include a regenerator housing, aplurality of stages, and a field generator. The regenerator housing mayextend along an axial direction between a first end portion of theregenerator housing and a second end portion of the regenerator housing.The regenerator housing may define a chamber that extends longitudinallyalong the axial direction between the first and second end portions ofthe regenerator housing. The plurality of stages may be positionedwithin the regenerator housing. The plurality of stages may be arrangedsequentially along the axial direction from the first end portion to thesecond end portion. Each stage of the plurality of stages may include acaloric material having a caloric temperature peak. The plurality ofstages may be arranged so that the caloric temperature peaks of theplurality of stages increase along the axial direction according to apredetermined, non-linear curve. The field generator may be positionedadjacent to the plurality of stages to subject the plurality of stagesto a variable field generated by the field generator.

In another exemplary aspect of the present disclosure, a refrigeratorappliance is provided. The refrigerator appliance may include a cabinetdefining a chilled chamber; and a heat pump system operable to cool thechilled chamber. The heat pump system may include a hot side heatexchanger, a cold side heat exchanger, a pump, and a caloric heat pump.The pump may be operable to flow a working fluid between the hot andcold side heat exchangers. The caloric heat pump may include aregenerator housing, a plurality of stages, and a field generator. Theregenerator housing may extend along an axial direction between a firstend portion of the regenerator housing and a second end portion of theregenerator housing. The regenerator housing may define a chamber thatextends longitudinally along the axial direction between the first andsecond end portions of the regenerator housing. The plurality of stagesmay be positioned within the regenerator housing. The plurality ofstages may be arranged sequentially along the axial direction from thefirst end portion to the second end portion. Each stage of the pluralityof stages may include a caloric material having a caloric temperaturepeak. The plurality of stages may be arranged so that the calorictemperature peaks of the plurality of stages increase along the axialdirection according to a predetermined, non-linear curve. The fieldgenerator may be positioned adjacent to the plurality of stages tosubject the plurality of stages to a variable field generated by thefield generator.

These and other features, aspects and advantages of the presentinvention will become better understood with reference to the followingdescription and appended claims. The accompanying drawings, which areincorporated in and constitute a part of this specification, illustrateembodiments of the invention and, together with the description, serveto explain the principles of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

A full and enabling disclosure of the present invention, including thebest mode thereof, directed to one of ordinary skill in the art, is setforth in the specification, which makes reference to the appendedfigures.

FIG. 1 provides a perspective view of a refrigerator appliance accordingto exemplary embodiments of the present disclosure.

FIG. 2 provides a schematic view of certain components of a heat pumpsystem positioned in the exemplary refrigerator appliance of FIG. 1.

FIG. 3 provides a perspective view of a heat pump according to exemplaryembodiments of the present disclosure.

FIG. 4 provides an exploded perspective view of the exemplary heat pumpof FIG. 3.

FIG. 5 provides a cross-sectional view of the exemplary heat pump ofFIG. 3.

FIG. 6 provides a front perspective view of the exemplary heat pump ofFIG. 3.

FIG. 7 provides a schematic representation of various steps in the useof a stage of the exemplary heat pump of FIG. 3.

FIG. 8 provides a chart of change in energy over temperature,illustrating caloric temperature ranges for several exemplary stages ofcaloric material as further described below.

FIG. 9 provides a chart of caloric temperature peak over a normalizedlongitudinal position (e.g., an axial direction), illustrating multiplenon-linear curves for several exemplary stages of caloric material asfurther described below.

DETAILED DESCRIPTION

Reference now will be made in detail to embodiments of the invention,one or more examples of which are illustrated in the drawings. Eachexample is provided by way of explanation of the invention, notlimitation of the invention. In fact, it will be apparent to thoseskilled in the art that various modifications and variations can be madein the present invention without departing from the scope or spirit ofthe invention. For instance, features illustrated or described as partof one embodiment can be used with another embodiment to yield a stillfurther embodiment. Thus, it is intended that the present inventioncovers such modifications and variations as come within the scope of theappended claims and their equivalents.

As used herein, the term “or” is generally intended to be inclusive(i.e., “A or B” is intended to mean “A or B or both”). The terms“first,” “second,” and “third” may be used interchangeably todistinguish one component from another and are not intended to signifylocation or importance of the individual components.

The present subject matter may be utilized in a caloric heat pump systemfor heating or cooling an appliance, such as a refrigerator appliance.While described in greater detail below in the context of amagneto-caloric heat pump system, one of skill in the art using theteachings herein will recognize that other suitable caloric materialsmay be used in a similar manner to heat or cool an appliance (i.e.,apply a field, move heat, remove the field, move heat). For example,electro-caloric material heats up and cools down within increasing anddecreasing electric fields. As another example, elasto-caloric materialheats up and cools down when exposed to increasing and decreasingmechanical strain. As yet another example, baro-caloric material heatsup and cools down when exposed to increasing and decreasing pressure.Such materials and other similar caloric materials may be used in placeof or in addition to the magneto-caloric material described below toheat or cool liquid/water within an appliance. Thus, caloric material isused broadly herein to encompass materials that undergo heating orcooling when exposed to a changing or variable field from a fieldgenerator, where the field generator may be a magnet, an electric fieldgenerator, an actuator for applying mechanical stress or pressure, etc.

Referring now to FIG. 1, an exemplary embodiment of a refrigeratorappliance 10 is depicted as an upright refrigerator having a cabinet orcasing 12 that defines a number of internal storage compartments orchilled chambers. In particular, refrigerator appliance 10 includesupper fresh-food compartments 14 having doors 16 and lower freezercompartment 18 having upper drawer 20 and lower drawer 22. Drawers 20,22 are “pull-out” type drawers in that they can be manually moved intoand out of freezer compartment 18 on suitable slide mechanisms.Refrigerator 10 is provided by way of example only. Other configurationsfor a refrigerator appliance may be used as well including applianceswith only freezer compartments, only chilled compartments, or othercombinations thereof different from that shown in FIG. 1. In addition,the heat pump and heat pump system of the present disclosure is notlimited to refrigerator appliances and may be used in other applicationsas well (e.g., air-conditioning, electronics cooling devices, etc.).Thus, it should be understood that while the use of a heat pump and heatpump system to provide cooling within a refrigerator is provided by wayof example herein, the present disclosure may also be used to providefor heating applications as well.

FIG. 2 is a schematic view of various components of refrigeratorappliance 10, including a refrigeration compartment 30 and a machinerycompartment 40. Refrigeration compartment 30 and machinery compartment40 include a heat pump system 52 having a first or cold side heatexchanger 32 positioned in refrigeration compartment 30 for the removalof heat therefrom. A heat transfer fluid such as, for example, anaqueous solution, flowing within first heat exchanger 32 receives heatfrom refrigeration compartment 30 thereby cooling contents ofrefrigeration compartment 30. A fan 38 may be used to provide for a flowof air across first heat exchanger 32 to improve the rate of heattransfer from refrigeration compartment 30.

The heat transfer fluid flows out of first heat exchanger 32 by line 44to heat pump 100. As will be further described herein, the heat transferfluid receives additional heat from caloric material in heat pump 100and carries this heat by line 48 to pump 42 and then to second or hotside heat exchanger 34. Heat is released to the environment, machinerycompartment 40, or other location external to refrigeration compartment30 using second heat exchanger 34. A fan 36 may be used to create a flowof air across second heat exchanger 34 and thereby improve the rate ofheat transfer to the environment. Pump 42 connected into line 48 causesthe heat transfer fluid to recirculate in heat pump system 52. Motor 28may be in mechanical communication with heat pump 100, as describedbelow.

From second heat exchanger 34, the heat transfer fluid returns by line50 to heat pump 100 where, as will be further described below, the heattransfer fluid loses heat to the caloric material in heat pump 100. Thenow colder heat transfer fluid flows by line 46 to first heat exchanger32 to receive heat from refrigeration compartment 30 and repeat thecycle as just described.

Heat pump system 52 is provided by way of example only. Otherconfigurations of heat pump system 52 may be used as well. For example,lines 44, 46, 48, and 50 provide fluid communication between the variouscomponents of heat pump system 52 but other heat transfer fluidrecirculation loops with different lines and connections may also beemployed. For example, pump 42 can also be positioned at other locationsor on other lines in system 52. Still other configurations of heat pumpsystem 52 may be used as well.

FIGS. 3 through 6 depict various views of an example heat pump 100 ofthe present invention. Heat pump 100 includes a regenerator housing 102that extends longitudinally along an axial direction between a first endportion 118 and a second end portion 120. The axial direction is definedby axis A-A about which regenerator housing 102 rotates. A radialdirection R is defined by a radius extending orthogonally from the axisof rotation A-A (FIG. 5). A circumferential direction is indicated byarrows C.

Regenerator housing 102 defines one or more chambers 104 that extendslongitudinally along the axial direction defined by axis A-A. Forexample, chamber 104 may extend along the axial direction defined byaxis A-A between first and second end portions 118, 120 of regeneratorhousing 102. Chamber 104 may also extend along circumferential directionC about the axis A-A. Alternatively, multiple chambers 104 may beposition proximate or adjacent to each other along circumferentialdirection C. Chamber 104 includes a pair of openings 106, 108 positionedat opposing end portions 118, 120 of regenerator housing 102.

Heat pump 100 also includes a working unit 112 that include caloricmaterial. Working unit 112 is located in a chamber 104 and extends alongthe axial direction A-A (e.g., between first and second end portions118, 120 of regenerator housing 102).

In certain embodiments, working unit 112 also extends alongcircumferential direction C about the axis A-A. Thus, working unit 112may have a cylindrical shape that is complementary to or fills chamber104. In particular, working unit 112 may have a cylindrical innersurface 130 and a cylindrical outer surface 132 that are spaced alongthe radial direction R. Working unit 112 may be a single, unitary pieceof caloric material in certain example embodiments. Thus, regeneratorhousing 102 may not include baffles or walls that separate the workingunit 112 into sections.

In alternative embodiments, working unit 112 is provided as a pluralityof discrete, fluidly-isolated segments that each include a caloricmaterial. Each segment of such working unit 112 may be located in aseparate chamber 104 and extend along axial direction A-A. Thus, two ormore segments of working unit 112 may be positioned adjacent to eachother along the circumferential direction C and extend longitudinallyalong the axial direction A-A.

Regenerator housing 102 defines a cavity 128 that is positioned radiallyinward of the chamber 104 and extends along the axial direction betweenfirst and second end portions 118, 120 of regenerator housing 102. Afield generator 126 (e.g., a magnet, an electric field generator, anactuator for applying mechanical stress or pressure, etc.) is positionedwithin cavity 128 and, for this example embodiment, extends along theaxial direction between first end 118 and second end portion 120. Fieldgenerator 126 provides a variable field (e.g., a magnetic field, anelectrical field, a mechanical strain field, a pressure field, etc.)that is directed radially outward as indicated by arrows M in FIG. 5. Inexemplary embodiments, field generator 126 may be configured as anelectromagnet or a combination of an electromagnet and one or moremagnets—each of which can be configured to generate a magnetic field(e.g., having a constant or variable magnetic flux along the axialdirection A-A).

The positioning and configuration of field generator 126 is such thatonly a portion of working unit 112 (or a subset of the plurality ofsegments) is within field M at any one time. For example, as shown inFIG. 5, about half of working unit 112 is within the field M while theremainder of working unit 112 is positioned remote from or outside ofthe field M created by field generator 126. However, as regeneratorhousing 102 is continuously rotated along the circumferential directionas shown by arrow W, the portion of working unit 112 within the field Mwill continuously change as some of working unit 112 will enter field Mand another portion of working unit 112 will exit the field M.

A pair of valves or seals 136, 138 is provided such that the seals 136,138 are positioned in an opposing manner at the first and second endportions 118, 120 of regenerator housing 102. More particularly, a firstseal 136 is positioned at first end portion 118 and a second seal 138 ispositioned at second end 120. First seal 136 has a first inlet port 140and a first outlet port 142. The ports 140, 142 of first seal 136 arepositioned adjacent to opening 106 of chamber 104. As shown, ports 140,142 are positioned one hundred eighty (180) degrees apart about thecircumferential direction C of first seal 136. However, otherconfigurations may be used. For example, ports 140, 142 may bepositioned within a range of about one hundred seventy (170) degrees toabout one hundred ninety (190) degrees about the circumferentialdirection C as well.

Second seal 138 has a second inlet port 144 and a second outlet port146. The ports 144, 146 of second seal 138 are positioned adjacent toopening 108 of chamber 104. As shown, ports 144, 146 are positioned onehundred eighty (180) degrees apart about the circumferential direction Cof second seal 138. However, other configurations may be used. Forexample, ports 144, 146 may be positioned within a range of about onehundred seventy (170) degrees to about one hundred ninety (190) degreesabout the circumferential direction C as well. Ports 144, 146 areconnected with lines 50, 48 (FIG. 1), respectively. As such, therotation of regenerator housing 102 about axis A-A sequentially placeslines 48, 50 in fluid communication with the channels within the caloricmaterial of working unit 112 as will be further described. Notably, atany one time during rotation of regenerator housing 102, lines 46, 50may each be in fluid communication with at least channel 150 within thecaloric material of working unit 112 while lines 44, 48 may also be influid communication with at least one other channel 150 within thecaloric material of working unit 112 about one hundred eighty (180)degrees away along the circumferential direction.

A heat transfer fluid may flow into chamber 104 through inlet ports 140,144 of seals 136, 138 so as to flow through the caloric material inworking unit 112 and then exit through outlet ports 142, 146 of seals136, 138. A reverse path can be used for flow of the heat transfer fluidin the opposite direction through the working unit 112. Seals 136, 138may be positioned relative to regenerator housing 102 such that workingfluid flows through channels 150 within working unit 112 when alignedwith ports of seals 136, 138. Tight clearances between seals 136, 138and working unit 112 may allow working fluid flow to only pass throughchannels 150 adjacent or aligned with ports 140 through 146. Regeneratorhousing 102 may be rotatable relative to first and second seal 136, 138.Ports 140, 142 are connected with lines 44, 46 (FIG. 1), respectively.As such, the rotation of regenerator housing 102 about axis A-Asequentially places lines 44, 46 in fluid communication with channelswithin the caloric material of working unit 112 as will be furtherdescribed.

FIG. 7 illustrates an exemplary method of the present disclosure using aschematic representation of a portion of working unit 112 of caloricmaterial in regenerator housing 102 as it rotates in the direction ofarrow W between positions 1 through 8 as shown in FIG. 6. During step200, the portion of working unit 112 is fully within field M, whichcauses the moments of the material to orient and the caloric material toheat as part of the caloric effect. Ordering of the field is created andmaintained as the portion of working unit 112 is rotated sequentiallythrough positions 2, 3, and then 4 (FIG. 6) as regenerator housing 102is rotated in the direction of arrow W. During the time at positions 2,3, and 4, the heat transfer fluid dwells in the caloric material of theportion of working unit 112 and, therefore, is heated.

In step 202, as regenerator housing 102 continues to rotate in thedirection of arrow W, the portion of working unit 112 will eventuallyreach position 5 (FIG. 6). As shown in FIGS. 3 and 6, at position 5 theheat transfer fluid can flow through the material as inlet port 140 infirst seal 136 is aligned with the channels 150 within the portion ofworking unit 112 while outlet port 146 in second seal 138 at the secondend portion 120 is also aligned with the channels 150 within the portionof working unit 112. As indicated by arrow Q_(H-OUT), heat transferfluid in the portion of working unit 112, now heated by the caloricmaterial, can travel out of regenerator housing 102 and along line 48 tothe second heat exchanger 34 (FIG. 2). At the same time, and asindicated by arrow Q_(H-IN), heat transfer fluid from first heatexchanger 32 (FIG. 2) flows into the portion of working unit 112 fromline 44 when working unit 112 is at position 5. Because heat transferfluid from the first heat exchanger 32 is relatively cooler than thecaloric material in working unit 112, the caloric material will loseheat to the heat transfer fluid.

Referring again to FIG. 7 and step 204, as regenerator housing 102continues to rotate in the direction of arrow W, the portion of workingunit 112 is moved sequentially through positions 6, 7, and 8 (FIG. 6)where the portion of working unit 112 is completely or substantially outof field M. The absence or lessening of the field M is such that themoments of the material become disordered and the caloric materialabsorbs heat as part of the caloric effect. During the time in positions6, 7, and 8, the heat transfer fluid dwells in the caloric material ofthe portion of working unit 112 and, therefore, is cooled by losing heatto the caloric material as the moments disorder. More specifically, theheat transfer fluid does not flow through working unit 112 because theopenings 106, 108, 122, and 124 corresponding to working unit 112 whenin positions 6, 7, and 8 are not aligned with any of the ports 140, 142,144, or 146.

Referring to step 206 of FIG. 7, as regenerator housing 102 continues torotate in the direction of arrow W, the portion of working unit 112 willeventually reach position 1 (FIG. 6). As shown in FIGS. 3 and 6, atposition 1 the heat transfer fluid in the portion of working unit 112can flow through the material as inlet port 144 in second seal 138 isaligned with the channels 150 within the portion of working unit 112while outlet port 142 in first seal 136 is also aligned with thechannels 150 within the portion of working unit 112. As indicated byarrow Q_(C-OUT), heat transfer fluid in the portion of working unit 112,now cooled by the caloric material, can travel out of regeneratorhousing 102 and along line 46 to the first heat exchanger 32 (FIG. 2).At the same time, and as indicated by arrow Q_(C-IN), heat transferfluid from second heat exchanger 34 (FIG. 2) flows into the portion ofworking unit 112 from line 50 when the portion of working unit 112 is atposition 5. Because heat transfer fluid from the second heat exchanger34 is relatively warmer than the caloric material in the portion ofworking unit 112 at position 5, the caloric material will lose some ofits heat to the heat transfer fluid. The heat transfer fluid now travelsalong line 46 to the first heat exchanger 32 to receive heat and coolthe refrigeration compartment 30 (FIG. 2).

As regenerator housing 102 is rotated continuously, the above describedprocess of placing each portion of working unit 112 in and out of fieldM is repeated. Additionally, the size of field M and regenerator housing102 are such that one portion of working unit 112 may be within thefield M at any given time during rotation. Similarly, the remainder ofthe working unit 112 may be outside (or substantially outside) of thefield M at any given time during rotation. Additionally, at any giventime, there may be only a portion of working unit 112 through which theheat transfer fluid is flowing while the remainder of working unit 112remains in a dwell mode. More specifically, while one portion of workingunit 112 is losing heat through the flow of heat transfer fluid atposition 5, another portion of working unit 112 is receiving heat fromthe flowing heat transfer fluid at position 1, while all remainingportions of working unit 112 are in dwell mode. As such, the system canbe operated continuously to provide a continuous recirculation of heattransfer fluid in heat pump system 52 as working unit 112 rotatesthrough positions 1 through 8.

As will be understood by one of skill in the art using the teachingsdisclosed herein, the number of ports in seals 136, 138 or otherparameters can be varied to provide different configurations of heatpump 100 while still providing for continuous operation. For example,each valve could be provided within two inlet ports and two outlet portsso that heat transfer fluid flows through at least four portions ofworking unit 112 at any particular point in time. Alternatively,regenerator housing 102 or seals 136, 138 could be constructed so that,for example, at least two portions of working unit 112 are in fluidcommunication with an inlet port and outlet port at any one time. Otherconfigurations may be used as well.

Accordingly, as shown in FIG. 7, each working unit 112 can be providedwith stages 152, 154, 156, 158, 160, and 162 of different caloricmaterials that are arranged sequentially along a predetermined direction(e.g., along axial direction A-A in this exemplary embodiment). Eachsuch stage includes a caloric material that exhibits the caloric effectat a different temperature or a different temperature range than anadjacent stage along the axial direction A-A. The range of temperatureover which the caloric material (normal or inverse) in each stageexhibits the desired caloric response to provide heating or cooling isreferred to herein as the “caloric temperature range.” In the case of amagneto-caloric material, this may also be referenced as the “Curietemperature range.” The temperature at which the caloric material ineach stage exhibits its maximum caloric effect (i.e., peak change inenergy) is referred to herein as the “caloric temperature peak.” In thecase of a magneto-caloric material, this may also be referenced as the“Curie temperature peak.”

The stages (e.g., 152, 154, 156, 158, 160, and 162) can be arranged tothat the caloric temperature ranges (e.g., Curie temperature ranges) ofthe plurality of stages increases along a predetermined direction suchas axial direction A-A (FIG. 3). For example, stage 152 may exhibit themagnet caloric effect at a temperature less than the temperature atwhich stage 154 exhibits the magnet caloric effect, which may be lessthan such temperature for stage 156, and so on. By configuring theappropriate number and sequence of stages of caloric material (e.g.,MCM), heat pump 100 can be operated over a substantial range of ambienttemperatures.

A motor 28 (FIG. 2) is in mechanical communication with regeneratorhousing 102 (FIG. 3) and provides for rotation of housing 102 about axisA-A. By way of example, motor 28 may be connected directly with housing102 by a shaft or indirectly through a gear box. Other configurationsmay be used as well.

In exemplary embodiments, the caloric temperature ranges of stages(e.g., 152, 154, 156, 158, 160, and 162) are selected to overlap inorder to facilitate heat transfer.

Such an overlap is illustrated in FIG. 8, which provides a chart ofchange in energy over temperature for several exemplary stages ofcaloric material (e.g., C8-1, C8-2, C8-3, C8-4, C8-5, C8-6, C8-7, C8-8,C8-9, and C8-10). Specifically, FIG. 8 provides a plot of the amount oftemperature change (ΔT) (e.g., in units of Kelvin) for stages ofdifferent caloric materials as a function of operating temperature T(e.g., in units of Kelvin). Similar to the arrangement of FIG. 7, eachsequential stage (e.g., C8-1 through C8-10) is longitudinally sequential(e.g., along the axial direction A-A). For example, C8-1 may representan initial stage, such as 152 (FIG. 7), while C8-3 represents alongitudinally-adjacent stage, such as 154 (FIG. 7). Moreover, C8-4 mayrepresent a further stage, such as 156 (FIG. 7) that islongitudinally-adjacent to C8-3, and so on. As shown, the calorictemperature range (e.g., Curie temperature range) for one stage (e.g.,C8-1 through C8-10) may overlap or coincide with at least a portion ofthe caloric temperature range for the stage(s) that is/are adjacent tothat one stage (e.g., adjacent along the axial direction A-A—FIG. 3).

At stated, different types or alloys of caloric materials can havedifferent caloric temperature ranges over which the caloric materialwill substantially exhibit a caloric effect (e.g., magneto-caloriceffect). In addition, the caloric temperature peak can also be differentfor different caloric materials. In exemplary embodiments, such as thoseshown in FIG. 8, the caloric temperature peaks may increase sequentially(e.g., along the axial direction A-A—FIG. 3).

Turning especially to FIG. 9, a chart is provided illustrating exemplarycaloric temperature peaks (e.g., in units Kelvin), such as Curietemperature peaks, defined by the adjacent stages of caloric materialalong the axial direction A-A (FIG. 3) (e.g., as a relative scale ofnormalized longitudinal position between 0 and 1). Specifically, twodiscrete embodiments are illustrated at C9-1 and C9-2, respectively.Each curve C9-1 and C9-2 represents a plot of a discrete set of stagesof caloric material that are arranged sequentially (e.g., as shown withstages 152-162 in FIG. 7). Thus, C9-1 represents a separateembodiment/configuration from C9-2. In the exemplary plottedembodiments, the horizontal axis (i.e., Normalized LongitudinalPosition) represents the working unit 112 (FIG. 3) along the axialdirection A-A, which is evenly distributed from the first end portion(i.e., 0 in the horizontal axis of Normalized Longitudinal Position) tothe second end portion (i.e., 1 in the horizontal axis NormalizedLongitudinal Position). Each plotted point on C9-1 and C9-2 indicates acaloric temperature peak for a discrete stage of caloric material. Inother words, each dot may represent a unique stage of caloric materiallocated at the normalized longitudinal position. Thus, T₀ on FIG. 9indicates a value of caloric temperature peak at the first end portion118 (FIG. 3), and T₁ indicates a value of caloric temperature peak atthe second end portion 120 (FIG. 3).

As shown, a plurality of stages of the regenerator 112 (FIG. 3) may bearranged so that the caloric temperature peaks of the plurality ofstages increase along the axial direction A. When assembled, the stages(i.e., the plotted peaks of each stage) form a predetermined, non-linearcurve (e.g., C9-1 or C9-2) along the axial direction. Thus, the overallincrease in caloric temperature peaks for the stages may be non-linear.

In optional embodiments, the non-linear curve (e.g., C9-1 or C9-2) mayexclusively increase. Thus, each subsequent stage may have a caloricmaterial that defines a caloric temperature peak that is equal to orgreater than the caloric material of the previous stage (e.g., from 0 to1 along the normalized longitudinal position or axial direction A-A).

In certain embodiments, the non-linear curve (e.g., C9-1 or C9-2) isprimarily controlled or set according to the selection of caloricmaterials between adjacent stages. In some such embodiments, each stageof the plurality of axial stages defines a common axial length. In otherwords, the length of each stage of caloric material may be equal inlength along the axial direction A-A (FIG. 3) (e.g., perpendicular tothe field generator 126). For instance, using FIG. 7 as a reference,each axial length L1, L2, L3, L4, L5, and L6 may be equal to each other.Thus, in order for the adjacent stages 152 through 162 to form anon-linear curve (e.g., C9-1 or C9-2—FIG. 9) caloric materials of eachstage (e.g., 152, 154, 156, 158, 160, 162) will be varied accordingly.

In alternative embodiments, the non-linear curve (e.g., C9-1 or C9-2) isfurther controlled or set according to a variation in axial lengthbetween one or more of the plurality of stages. One or more stages ofthe plurality of stages may thus define a discrete axial length that isunique from an axial length defined by another stage of the plurality ofstages. In other words, the length of at least one stage of caloricmaterial along the axial direction A-A may be different or unique fromthe length of another stage of caloric material. For instance, usingFIG. 7 as a reference, one or more of the axial lengths L1, L2, L3, L4,L5, or L6 may be different from another axial length L1, L2, L3, L4, L5,or L6. Thus, in order for the adjacent stages 152 through 162 to form anon-linear curve (e.g., C9-1 or C9-2—FIG. 9) axial length (e.g., L1, L2,L3, L4, L5, or L6), as well as the caloric material, of each stage(e.g., 152, 154, 156, 158, 160, 162) will be varied accordingly.

As illustrated in FIG. 9, the non-linear curve (e.g., C9-1 or C9-2)generally defines a curvature ratio (C_(r)) across the axial directionA-A. For example, the non-linear curve (e.g., C9-1 or C9-2) may berepresented as a polynomial equation, such asT=Ax+Bx ²  Eq. 1

wherein

T is the caloric temperature peak value;

x is the normalized longitudinal position value;

A=B−T_(max)−T_(min); and

B=C_(r)/(1−C_(r))*T_(max)

In the exemplary embodiments C9-1 and C9-2 of FIG. 9, T_(max) equal T₁,while T_(min) equals T₀. Thus, the curvature ratio C_(r) may a non-zerovalue that is either positive (as in the case of C9-1) or negative (asin the case of C9-2). The absolute value of the curvature ratio C_(r)may be greater than zero and less than one (i.e., 0<|C_(r)|<1). Incertain embodiments, the curvature ratio C_(r) is a non-zero valuebetween −0.5 and 0.5. In additional or alternative embodiments, thecurvature ratio C_(r) is a non-zero value between −0.1 and 0.1.

This written description uses examples to disclose the invention,including the best mode, and also to enable any person skilled in theart to practice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they include structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. A heat pump system, comprising a hot side heatexchanger; a cold side heat exchanger; a pump operable to flow a workingfluid between the hot and cold side heat exchangers; and a caloric heatpump comprising a regenerator housing extending along an axial directionbetween a first end portion of the regenerator housing and a second endportion of the regenerator housing, the regenerator housing defining achamber that extends longitudinally along the axial direction betweenthe first and second end portions of the regenerator housing, aplurality of stages positioned within the regenerator housing, theplurality of stages being arranged sequentially along the axialdirection from the first end portion to the second end portion, eachstage of the plurality of stages comprising a caloric material having acaloric temperature peak, the plurality of stages being arranged so thatthe caloric temperature peaks of the plurality of stages increase alongthe axial direction according to a predetermined, consistent, non-linearcurve, and a field generator positioned adjacent to the plurality ofstages to subject the plurality of stages to a variable field generatedby the field generator, wherein the predetermined, consistent,non-linear curve defines a curvature ratio between −0.5 and 0.5 definedfrom the first end portion to the second end portion.
 2. The heat pumpsystem of claim 1, wherein the field generator comprises a magnet. 3.The heat pump system of claim 1, wherein the field generator comprisesan electromagnet.
 4. The heat pump system of claim 1, wherein the fieldgenerator, the plurality of stages, or both, are configured for cyclingthe plurality of stages in and out of the variable field duringoperation of the heat pump.
 5. The heat pump system of claim 1, whereinthe field generator is axially fixed at a predetermined positionrelative to the first end portion and the second end portion.
 6. Theheat pump system of claim 1, wherein each caloric material of theplurality of stages comprises a caloric temperature range, and whereinthe caloric temperature ranges of the plurality of stages overlapbetween stages that are adjacent along the axial direction.
 7. The heatpump system of claim 1, wherein the predetermined, consistent,non-linear curve defines a curvature ratio between −0.1 and 0.1.
 8. Theheat pump system of claim 1, wherein each stage of the plurality ofstages defines a common axial length.
 9. The heat pump system of claim1, wherein one or more stages of the plurality of stages defines adiscrete axial length that is unique from an axial length defined byanother stage of the plurality of stages.
 10. A refrigerator appliance,comprising: a cabinet defining a chilled chamber; and a heat pump systemoperable to cool the chilled chamber, the heat pump system comprising acold side heat exchanger positioned at the chilled chamber; a hot sideheat exchanger positioned outside the chilled chamber; a pump operableto flow a working fluid between the hot and cold side heat exchangers;and a caloric heat pump comprising: a regenerator housing extendingalong an axial direction between a first end portion of the regeneratorhousing and a second end portion of the regenerator housing, theregenerator housing defining a chamber that extends longitudinally alongthe axial direction between the first and second end portions of theregenerator housing, a plurality of stages positioned within theregenerator housing, the plurality of stages being arranged sequentiallyalong the axial direction from the first end portion to the second endportion, each stage of the plurality of stages comprising a caloricmaterial having a caloric temperature peak, the plurality of stagesbeing arranged so that the caloric temperature peaks of the plurality ofstages increase along the axial direction according to a predetermined,consistent, non-linear curve, and a field generator positioned adjacentto the plurality of stages to subject the plurality of stages to avariable field generated by the field generator, wherein thepredetermined, consistent, non-linear curve defines a curvature ratiobetween −0.5 and 0.5 defined from the first end portion to the secondend portion.
 11. The refrigerator appliance of claim 10, wherein thefield generator comprises a magnet.
 12. The refrigerator appliance ofclaim 10, wherein the field generator comprises an electromagnet. 13.The refrigerator appliance of claim 10, wherein the field generator, theplurality of stages, or both, are configured for cycling the pluralityof stages in and out of the variable field during operation of the heatpump.
 14. The refrigerator appliance of claim 10, wherein the fieldgenerator is axially fixed at a predetermined position relative to thefirst end portion and the second end portion.
 15. The refrigeratorappliance of claim 10, wherein each caloric material of the plurality ofstages comprises a caloric temperature range, and wherein the calorictemperature ranges of the plurality of stages overlap between stagesthat are adjacent along the axial direction.
 16. The refrigeratorappliance of claim 10, wherein the predetermined, consistent, non-linearcurve defines a curvature ratio between −0.1 and 0.1.
 17. Therefrigerator appliance of claim 10, wherein each stage of the pluralityof stages defines a common axial length.
 18. The refrigerator applianceof claim 10, wherein one or more stages of the plurality of stagesdefines a discrete axial length that is unique from an axial lengthdefined by another stage of the plurality of stages.